There are a variety of plastic parts or products or components thereof which are made by depositing or pouring a resin into an open mold configuration. For this purpose, dispensers have been developed which combine the necessary chemicals for the particular application in a mixhead. In addition to a mixhead body where the requisite chemicals are combined, the mixhead is provided with a mixhead pour nozzle which dispenses a metered quantity of the combined chemicals into an open mold during each pouring cycle of the molding process.
In a great many instances, it is possible to effect a pour cycle without encountering problems in the retention and build-up of chemicals at the outlet of a mixhead pour nozzle. This may be accomplished through a number of approaches. The design of the mixhead pour nozzle and the mixhead plunger operative therein may be significant in achieving a pour cycle without residual chemicals remaining on or building up on the mixhead pour nozzle. In other instances, the selection and compounding of the chemicals employed in the molding process may be tailored such that tendencies for adhesion of the chemicals and the resultant build-up is largely eliminated or sufficiently reduced such as not to present a problem with respect to the necessity for cleaning residual chemicals from the mixhead pour nozzle.
In some instances, build-up of a molding chemical on a mixhead pour nozzle cannot be controlled by the chemicals employed or the design of the mixhead or the mixhead pour nozzle alone. For example, in certain applications involving the reaction injection molding of urethane foams, the compounded foam as emitted from the mixhead pour nozzle has a tacky, adhesive quality which promotes adherence to and build-up of the foam on the mixhead pour nozzle such as to require cleaning on an extremely frequent basis to maintain proper operation of the mixhead pour nozzle.
The creation of a tacky or adhesive quality of the foam may result from a number of factors. For example, some water-blown foams tend to produce a foam that at the time it is poured from the mixhead pour nozzle is relatively soft and tacky and which becomes very rigid in a relatively short period of time. Such foams are particularly susceptible to retention on a mixhead pour nozzle and rapid accumulation to the point of adversely interfering with the pouring operation of the nozzle. Foams having tacky adhesive qualities are also known to result from the use of certain polyols and additives. In some instances, the use of foams having such adhesive qualities is necessary to achieve a part or product having particular characteristics, despite the difficulties encountered with foam retention and build-up on a mixhead pour nozzle.
The prior art reflects a number of approaches to preventing the build-up of foams, sealing compounds, or other similar materials on various types of nozzle configurations. In some instances, various types of portable blow-off nozzles or air knives are used in the industry for cleaning, washing, and removing excess material from spray guns or other nozzle configurations. While perhaps suitable for intermittent cleaning operations, these devices have definite disadvantages and shortcomings in regard to materials, such as foams, having tacky, adhesive qualities. The manual use of blow-off nozzles or air knives is highly labor-intensive. In addition, the fixed mounting or manual directioning of air knives or blow-off nozzles has the disadvantage that it tends to blow the residual material on a nozzle laterally on the mold, often causing contamination of the fixtures, mold carriers, or related conveying systems which may be employed.
Another approach to the cleaning of nozzles involves basically the internal cleaning of the nozzle. In such instances, suitable valving is provided to direct air or a cleaning solvent through selected passages internally of the nozzle to follow at least a portion of the travel path of the resins and catalysts to clean the mixing chambers and passages internally of the nozzles. Besides the additional complexity, expense, and operational drawbacks of such internal cleaning apparatus, such may be ineffective to remove foam or other materials which may accumulate on the head of a nozzle located radially outwardly of an orifice therein.
There are also numerous examples of the use of blow-off nozzles which issue a jet of air that is generally circular in cross-section and parallel to the blow-off nozzle axis. Various types of direct and induced air flow have been provided to effect essentially a conical or annular air flow substantially paralleling the axis of the nozzle and positioned from a location radially proximate to or even displaced a distance from the nozzle. These devices, however, normally have little effectiveness in removing materials which are significantly adhered to a radial surface constituting the nose of the nozzle which is displaced proximate to or outwardly of the orifice therein. In addition, some of these devices may be prone to scattering material which may be displaced with an extent of contamination of surrounding elements. No single solution to the displacement of molding material adhered to a pour nozzle has eliminated all of the various disadvantages heretofore experienced in usage of the various devices employed in the prior art.